function [fu,dfu,sfu]=nonlinear_terms(u)
global c a_t b p e t n_t n_p x_t y_t ar nth0 pwr;

%    -1/c*\delta u(x)+a_t(x)*u(x)-f(x,u(x))=0.     a_t\ge 0.
fu=u.^pwr;                 %fu=f(x,u(x)), pwr is given in initial.m
dfu=pwr*u.^(pwr-1);        %d f(x,u)/du
sfu=u.^(pwr+1)/(pwr+1);    %anti-derivative of f(x,u) w.r.t. u
%fu=u-sin(u);
%dfu=1-cos(u);
%sfu=0.5*u.^2+cos(u);
